Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

this often requies flex duct being taken off collars
to seal completely and 3/4 around collar to plenum.
inner liner mastic sealed,
insulation and outer liner in full contact with plenum/supply box
and mastic sealed.

its a bit more that as best as they can where accessable.
it is worth making access.

I too am concerned about the "helper". I am not 100% sure I am getting through to the contractor on the importance of sealing the existing ducts.

We don't have any flex duct connections - all take-offs are galvanized hard metal duct and main trunks are rectangular metal (all presently covered with duct insulation).

I am doing the register boxes myself - on the inside as far as I can reach in. But I have been using mastic "putty" to plug openings and aluminum foil tape (Reflectix) over joints. I will try and pick up some paint on mastic (hard to find here) and some mastic backed tape - I think I saw that somewhere here.

with the ducts being hard pipe there are more leakage sites.
you may have to settle for sealing take off at plenum,
unless unwrapping, sealing and re-insulating.
doesn't sound like this company would do this.

depending upon the amount of leakage it may or may not
be worthwhile.
unless you know the amount of leakage..its just a wag.
but you can get an idea with unit running and feeling
around the plenum for air movement. if you wet your
hand you can feel it better. not great...but shows
some leaks.

I've done it both ways..lots of leakage unwrap seal and rewrap
less leakage..takeoffs with paint mastic and boxes with mastic tape.
its backbreaking work..and doesn't come cheap.
not rocket science, but difficult. most companies don't have time
or inclination to do this kind of thing.

best of luck.

The cure of the part should not be attempted without the cure of the whole. ~Plato

It's very simple. I assume your main focus was on the new system. Duct sealing was not the first reason for the call. This task may have been brought up while looking at the old system or old ducts. The duct sealing needs to be part of the scope of what they are going do. It needs to be on the contract. All the visible duct wrap needs to be removed and all the duct sealed with mastic and then re-insulated. This needs to be in the contract.

It's very simple. I assume your main focus was on the new system. Duct sealing was not the first reason for the call. This task may have been brought up while looking at the old system or old ducts.

The above does more or less sum it up.

Our contractor is honestly trying to help by providing a low cost way of sealing. But it may not be the best way.

In the end, I suppose it comes down to economics. If my BB heating cost is $2400 and the heat pump theoretically reduces it to say $1200. Then how much should I spend on duct sealing to make sure we get the saving? What sort of saving might I get given about 75ft of rectangular supply duct (14x10, 10x10) and about 60ft of 6/7 in round duct is accessible and represents about 75% of total ductwork.

One other question - Our energy auditor sugested we strip the ducts and have then sprayed with PU foam. Seal and insulate in one step. Is this a viable option?

Blower door test, will give you some numbers, then you need a duct sealing process

We will have blower door test done again as part of our required eCoEnergy before and after audit. It will show if we have duct leakage. I may try and get them to allow me to block all registers/returns and see what the difference is.

Post pictures of the ducts so we can see. No biggie, but fun to look at. If we see something outta sorts, we'll give you a heads up.

OK, here are some pics. In the layout, the orange ducts are in an enclosed kneewall and are not accessible. They and the other main trunks are rectangular. All branches round like one in pic. The return ducts will be redone to suit new air handler.

Looks like lots of opportunity there for tightening your ducts,as you already know.
Can't believe the original installer didn't even try with duct tape.

These were A/C ducts installed in late 60's and intended for use just for the few weeks of really hot weather that we get in summer. I don't suppose they cared much about a bit of leakage back then when electricity was cheap and usage would be minimal.

But now we want to use those same ducts for heat pump. Average COP for heating season is predicted to be about 2.0. But we won't see that unless we minimize leakage of air and heat losses.

Do you think we should have contractor's helper strip main trunk ducts as well as branches? Once sealed, is there a better way of holding duct insulation in place than the strings they used?

the strings worked pretty well back in the day.
I've untied a few duct systems insulated this way.

one of the things to see as you unwrap is if they
screwed the joints together. adding 3 screws really holds
the pieces together and makes the duct system's strength.
sometimes the pieces are just duct taped. and duct tapes fail.

looking at the pics..there are screws. just make sure that all joints
are screwed. these joints along with long seams are the leakage areas.
as the plenum is unwrapped you'll see that the duct leakage corresponds
with the dirt trails on the insulation.

after screwing the pieces together, then mastic is applied.
it will take a day for it to set enough for it to be insulated.
R-8 duct wrap is what I use.
ductwrap is stapled in place with a duct stapler.
then the stapled seam is covered with foil scrim kraft (fsk) tape.

the staples should be used generously..staples are cheap.
if they are space too far apart they will not hold long term
I like a double row of staples about an inch apart.
the fsk adds extra holding.

I'd do the whole thing..mastic re-wrap.
are the supply boxes insulated internally?
no insulation visible on exterior of box in pic.
that would be another area to seal and insulate.

has anything been mentioned about ducts being sized
correctly? in my area there are older homes with all
6" hard pipe that was installed for heating only.
makes a mess when cooling is added to system.

don't know if hvac company will do all the sealing work
and re-insulating without price going up. its a lot of work.

best of luck

The cure of the part should not be attempted without the cure of the whole. ~Plato

looking at the pics..there are screws. just make sure that all joints
are screwed.

It seems all joints in round ducts have three screws

ductwrap is stapled in place with a duct stapler.
then the stapled seam is covered with foil scrim kraft (fsk) tape.

Can't quite envisage how the stapler works, but hopefully contractor will have one!

I'd do the whole thing..mastic re-wrap.

OK I will hope we get that far - I will have them start on round branches and when they get that done, move to main trunks. The guy will be here for a day and I will pay him T&M.

are the supply boxes insulated internally?
no insulation visible on exterior of box in pic.
that would be another area to seal and insulate.

The boxes except for the uninsulated one I used in pics, do have external insulation and will be buried in attic insulation. Never thought about insulating on inside, but I don't think much could be added because registers have to push up inside boxes.

has anything been mentioned about ducts being sized
correctly? in my area there are older homes with all
6" hard pipe that was installed for heating only.
makes a mess when cooling is added to system.

I used HVAC-Calc to do room by room check. Ducts supplying registers vary in diameter by room - sizing seems OK. Main trunks were checked by heat pump contractor (and me!) they seem to be OK. Something like 0.4"wg for longest run.

don't know if hvac company will do all the sealing work
and re-insulating without price going up. its a lot of work.

It's T&M and they are using low cost helper while they are doing main Heat Pump work. At most 7hrs at $??/hr. I will see how it is going and cut them off if I am not satisfied with work.

Thanks very much for the input - Puts me in a better position to discuss with contractor. I think I might just seal the one duct I photographed myself and use that as an example of how the rest should be done. (it is easy to get at!)

As we should have known, the offer of a helper to work on the duct sealing has not worked out.

- We have 10 registers each supplied by a section of round hard duct. Each of these has a length of main trunk of 8-12ft associated with it.
- I had two branches sealed just with tape by attic insulator - I checked one of them and he had not put duct insulation back on - just piled batts over it. I was in there, so sealed again using paint on duct seal and put insulation back on. The otehr one is under cellulose, so insulator will be back and will put covers back on. Tape will have to do on that one.
- Before "helper" came, I had a weak moment and decided to crawl into the "tunnels" behind the attic kneewalls that I previosly considered inaccessible- I knew contractor wouldn't go in there, so I sealed joints in there too.
- I also sealed one branch and one trunk joint in main attic as an example for helper. By now, I had 5 of the 10 sections done.

As it turned out, they did not send a helper specifically for the sealing job. The ductwork and mechanical techs each had a helper and they were supposed to do the sealing in their spare time! Getting them to do it was like pulling teeth. After a full week, they had removed a good part of the insulation, but only sealed one branch and a few trunk seals.

Part of the job, was to install a new attic return duct. It's 20x14 and about 20ft with quite a number of joints. Sealing those was part of the contractor's job. On the weekend, I went in and had a look. The "helper" had sealed just the top and front of each seam - the ones that could be easily seen. The back and bottom of these rectangular seams had not been touched.

In frustration and because ducts were supposed to be insulated this week, I spent my Canadian Thanksgiving Monday lying on my back, bumping my head etc but got all those joints sealed. I also did one other section of the existing ducts. This leaves just two to go! Contractor says he will do them

What I have found, is that the contractor from project manager down just does not understand the importance of the duct sealing. They think I am being overly picky! Their installation is otherwise good, but.....

The insulation subcontractor also questioned why I would want R-12 on the ducts. He said outside walls have that much! I guess he didn't realize that attic ducts are outside walls! He has not been back to do teh work, but I don't have a good feeling that it will be dome properly without intervention.

From what I can see, our situation is much like many of you in the South would consider normal. Heat pump and ducts in unconditioned space and no basement. Up here most builders wisely don't build that way. Perhaps this is the reason that HVAC contractorsup here just don't understand?

Anyway, sorry for the rant! I am trying to work with the pros and much of the work has gone well. But the part I consider most important is not. I am 71 and shouldn't be doing DIY work like this, but it seems only way to get job done. We have had a warm Fall, but any day now temperatures will plunge.